How do I get the purple wonderful stone in Harvest Moon DS: Tale of Two Towns?

[ToManyQuestions]

I understand that on the game site, it tells you that you can fish at the Bluebell fishing area in the Winter on a snowy day...but the pond's frozen over all of winter and can't be fished in! So what do they want me to do? I'm so confused! Please help! T_T Thank you!